Genetic studies on the salt-resistant (R) and salt-sensitive (S) rats of Dahl will include: 1) further development of inbred sublines of R rats which either have or do not have the four pituitary colloid proteins (called R1, R2, R3, or R4) originally described in the R strain; 2) determination of the number of loci affecting pituitary colloid proteins in this model; 3) development of inbred S rats. Pituitary colloid proteins R4 (MW 235,000) and R3 (MW 130,000) will be isolated and characterized with respect to immunological similarities to lower molecular weight forms (R1 and R2). A radioimmunoassay for R3 protein will be developed since it is apparently unrelated to previously studied colloid proteins. If R3 can be measured in peripheral blood its response to various manipulations e.g. hypophysectomy, salt feeding, etc. will be studied.